To meet the demand for higher integration density and operating speed of LSIs, the effort to reduce the pattern rule is in rapid progress. The wide-spreading flash memory market and the demand for increased storage capacities drive forward the miniaturization technology. As the advanced miniaturization technology, manufacturing of microelectronic devices at the 65-nm node by the ArF lithography has been implemented in a mass scale. Manufacturing of 45-nm node devices by the next generation ArF immersion lithography is approaching to the verge of high-volume application. The candidates for the next generation 32-nm node include ultra-high NA lens immersion lithography using a liquid having a higher refractive index than water in combination with a high refractive index lens and a high refractive index resist film, extreme ultraviolet (EUV) lithography of 13.5 nm wavelength, and double patterning version of the ArF lithography, on which active research efforts have been made.
Besides the positive tone resist by alkaline development, a highlight is recently put on the negative tone resist by organic solvent development. It would be desirable if a very fine hole pattern, which is not achievable with the positive tone, is resolvable through negative tone exposure. To this end, a positive resist composition featuring a high resolution is subjected to organic solvent development to form a negative pattern. An attempt to double a resolution by combining two developments, alkaline development and organic solvent development is under study.
As the ArF resist composition for negative tone development with organic solvent, positive ArF resist compositions of the prior art design may be used. Such pattern forming processes are described in Patent Documents 1 to 6.
These patent documents disclose resist materials for organic solvent development comprising a copolymer of hydroxyadamantane methacrylate, a copolymer of norbornane lactone methacrylate, a copolymer of methacrylate having acidic groups including carboxyl, sulfo, phenol, thiol and other groups substituted with two or more acid labile groups, and a copolymer of methacrylate having a cyclic acid-stable group ester, and pattern forming processes using the same.
The ester unit having a carboxyl group protected with an acid labile group is one of predominant constituent units of base resins in currently available chemically amplified resist compositions. Patent Document 7 discloses a positive resist comprising units of hydroxyadamantane methacrylate having a hydroxyl group protected with a tertiary alkyl group. Also, Patent Document 8 discloses formation of a negative pattern via organic solvent development, using a base resin comprising those units having a hydroxyl group protected in acetal or tertiary ether form as the sole acid labile unit.
Polymerization units having such an acid labile group are important as constituent units of the base resin in the current chemically amplified resist compositions. In addition, polymerization units having an adhesive group are also important for forming patterns at high resolution when considered from the standpoints of dissolution contrast and acid diffusion control. These polymerization units include methacrylic compounds having lactone units of butyrolactone, valerolactone, norbornanelactone or cyclohexanelactone skeleton, and sultone units. Among others, adhesive units having butyrolactone skeleton which is a 5-membered lactone are mainly used, with a focus placed on α-methacryloyloxy-γ-butyrolactone and β-methacryloyloxy-γ-butyrolactone skeletons.
Patent Documents 9 and 10 disclose methods for the preparation of β-methacryloyloxy-γ-butyrolactone compounds having a substituent on lactone ring, and their use as resist material.